In Diablo 2 Resurrected, you can hire mercenaries controlled by the computer for gold, who will help you fight against monsters. On this page, you will find the answer to whether it is possible to resurrect them.
Hirelings become available after reaching Level 9 or after completing the task Sisters' Burial Grounds. In every city, there is someone responsible for hiring companions - in the first camp, it is Kashya. After the death of your ally, you can go to her to ask for someone new, maybe a higher level than yours?
However, if you've been traveling together for a while, advanced the level of your current companion, and equipped they with valuable equipment, a better idea would be resurrecting them. You pay for it with gold, and the price will rise with the level of your mercenary.